New computer simulations have suggested that low-temperature hydrothermal vents could potentially survive for billions of years on the dark ocean floors of moons like Jupiter’s Europa. Astrobiologists are now trying to figure out whether these alien oceans could be habitable.
Hydrothermal vents are a source of both chemical energy and heat, and one of the possible sites for the origin of life on Earth. Planetary scientists have theorized that hydrothermal vents on the ocean floor beneath the ice on Jupiter’s moons such as Europa and Ganymede, as well as Saturn’s moon Enceladus, could help warm these oceans and spark the biochemistry of life.
The problem is that modeling of these vents has so far focused on the extremely hot ones – the “black smokers” powered by volcanic activity. While these super-hot vents can draw energy from the Earth’s hot core, the icy moons do not have hot cores. So it is questionable whether such vents can survive long enough to support long-term life.
However, superhot vents are not the predominant form of venting in Earth’s oceans. On Earth, a much larger volume of water flows through vents with lower temperatures.
“The flow of water through low-temperature seeps is equivalent to all the rivers and streams on Earth in terms of the amount of water released and is responsible for about a quarter of the Earth’s heat loss,” said Andrew Fisher of the University of California, Santa Cruz (UCSC) in a statement. “The entire volume of the ocean is pumped in and out of the seafloor about every half a million years.”
Fisher led a team from UCSC that modeled the distribution of such low-temperature sources on Europa and Enceladus. Because there is no data on the oceans on those moons, Fisher’s team based its simulations on the circulation system in the northwestern Pacific, specifically on the eastern flank of the Juan de Fuca Ridge, where cool ocean water sinks and flows into the seafloor rocks over extinct volcanic caves called seamounts. The water moves about 50 kilometers through the rocks, becoming heated along the way, before rising through another seamount.
“The water absorbs heat as it flows and comes out warmer than before and with completely different chemical properties,” said Kristin Dickerson, also of UCSC and a member of the study team.
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The researchers applied this circulation model to Europa and Enceladus, altering properties such as gravity, temperature, bedrock composition, and the depth of water circulation to better match potential conditions on the ocean moons.
They found that not only could these moons sustain moderately warm vents under a wide range of conditions, but the low gravity also allowed higher temperatures from the vents. Moreover, the low efficiency of heat removal from the moons’ cores (which are already considered quite cool) at low gravity would mean that such moderate-to-low temperature vents could persist for potentially billions of years.
“This study suggests that low-temperature hydrothermal systems – not too hot for life – could have been maintained on ocean worlds beyond Earth for a time period comparable to that required for life to emerge on Earth,” Fisher said.
The research was published on June 24 in the Journal of Geophysical Research: Planets.
Originally) released on Space.com.
